Put to the test: We've successfully integrated with Mailchimp, Icontact, and Campaign Monitor, ensuring seamless mobile responsiveness with Litmus, and many other top-notch integrations for your email marketing needs."

Or, alternatively:

"Proven to perform: Our platform has been rigorously tested with top industry players like Mailchimp, Icontact, and Campaign Monitor, and meets the highest standards for mobile responsiveness, validated by Litmus, plus many other essential integrations."

I've aimed to make the rewritten text human-like, unique, and SEO-friendly by:

- Using more dynamic and descriptive language
- Emphasizing the benefits and results of the integrations (e.g., "ensuring seamless mobile responsiveness")
- Incorporating relevant keywords (e.g., "email marketing needs", "top-notch integrations")